Space-based surveillance systems use infrared detectors coupled to computerized data processors for monitoring heated objects and their movements in the atmosphere below and on the ground. The infrared spectrum covers a wide range of wavelengths, from about 0.75 micrometers to 1 millimeter. The function of infrared detectors is to respond to energy of a wavelength within some particular portion of the infrared region. Heated objects will dissipate thermal energy having characteristic wavelengths within the infrared spectrum. Different levels of thermal energy, corresponding to different sources of heat, are characterized by the emission of signals within different portions of the infrared frequency spectrum. Detectors are selected in accordance with their sensitivity in the range of interest to the designer. Similarly, electronic circuitry that receives and processes the signals from the infrared detectors is also selected in view of the intended detection function.
Current infrared detection systems incorporate arrays of large numbers of discrete, highly sensitive detector elements the outputs of which are connected to sophisticated processing circuity. By rapidly analyzing the pattern and sequence of detector element excitations, the system circuitry can identify and monitor sources of infrared radiation. The outputs of the detectors must undergo a series of processing steps in order to permit derivation of the desired information. The more fundamental processing steps include preamplification, tuned bandpass filtering, clutter and background rejection, multiplexing and fixed noise pattern suppression. By providing a detector connecting module that performs at least a portion of the signal processing functions within the module, i.e. on integrated circuit chips disposed adjacent the detector focal plane, the signal from each detector need be transmitted only a short distance before processing. As a consequence of such on-focal plane or “up front” signal processing, reductions in size, power and cost of the main processor may be achieved.
Up front signal processing also helps alleviate performance and reliability problems associated with manufacturing high packing density electronics assemblies. An important part of the up front data processing are temporal net and spatial nets for filtering the data and discarding false readings. Temporal nets simply compare the present frame of data in time to each of multiple past frames of data. More problematic, is setting up a spatial net to compare values from neighboring detector elements. Multiple paths of communication from each of the detector elements to several locations on the processing circuitry are difficult, especially if the several locations are on multiple chips in a multi-layer stack. A high number of criss-crossing electrical connections may also develop an electrical magnetic field that interferes with data transmission. It is desirable to provide a spatial net that accomplishes the necessary interconnects, while minimizing the complexity of the communication paths.
The prior art has attacked this problem by providing increasing numbers of miniaturized solder contacts on the edge of the chip stack through electron-beam lithography. Also, “optronic” components are under development that will provide for optical interconnections, but the level of miniaturization attained is not yet comparable to electronic components. Methods are needed with available technology that reduce the complexity of the interconnections.